The present invention relates to a method of manufacturing a color filter for use in a solid-state image sensor or a contact type image sensor such as charge coupled device(CCD) or bucket brigade device(BBD).
For a solid-state image sensor, a particular wave of light to be incident on a surface of the image sensor like CCD or BBD is selectively radiated in order to obtain a color, for which there has been made a color filter for color separation divided by red, green, blue or yellow, cyan, magenta. In this case, for a display device such as liquid crystal display(LCD), the receiving of light is just changed.
Currently, as a color filter, there is being widely adapted an organic dye type(or on-chip type) which obtains a desired spectrum characteristic in a manner that an easily dyed photosensitive resin is patternized by a photo-etching technique and the resultant pattern is dyed by a dyeing material.
The method of manufacturing such a conventional color filter which is formed on the charge coupled devices is now explained.
By way of an example therefor, it is preferably taken cross-sectional view of the image sensor of which the color filter is formed on an interline transfer charge coupled device(referred to as IT-CCD hereinbelow), as shown in FIG. 1. The conventional technique of FIG. 1 is described in Matsushidat technique report(90.6 vol.36. No. 3) and Nichei Micro Device(1989 December version).
Referring to FIG. 1, IT-CCD comprises photodiodes 32, 33, 34, 35, 36, 37 and 38 for optical-to-electrical converting the light to be incident on the surface of p-type semiconductor substrate, an active area having a charge-transfer part repeatedly arranged for transferring charges, the active area being adjacent to the photodiodes 32, 33, 34, 35, 36, 37 and 38, and a pad area having pad part 52 for externally transferring a signal, the pad area being adjacent to the active area.
The photodiodes 32-38 may have PNP structure by being formed on p-type semiconductor substrate 30 or PNPN structure in order to remove dark current.
The charge transfer part 50 comprises an insulating layer 44 of SiO.sub.2 for insulating a first conductive layer 42 of polycrystal silicon transferring charges, a second conductive layer 46 of polycrystal silicon formed on the insulating layer 44 and a light blocking layer 48 of dual layer of metal aluminium Al and SiW.sub.x formed on the second conductive layer 46.
On the IT-CCD, color filter is formed. First, on the entire surface of IT-CCD, a flat layer 40 is formed in order to form a uniformed color filter layer and to prevent the light blocking layer 48 and the metal pad part 52 as metal layers from being corroded due to the acid radical of a photosensitive material when a color pattern array(referred to as a color filter layer hereinafter) is dyed over the entire surface of IT-CCD. The flat layer 40 is formed of a positive polyimide having an excellent light transmissivity and a photo-sensitivity at a hardening temperature.
Thereafter, according to the conventional method for manufacturing color filter layer, a photo-sensitive layer having photo-sensitivity by using ammonium dichromate on hydrophile macromolecule material such as polyvinyl alcohol, casein or gelatine is evenly deposited. Then, after drying it, only the first color pattern portion is exposed and developed by mask exposing method, thereby forming a desired pattern.
By dyeing the pattern with a dyeing material having a predetermined spectrum characteristic, magenta layer of the first color filter layer 54 is formed at the position corresponding to the first photodiode 32.
Then, the second and the third color filter layers are formed in the same manner. A first inter-layer 56 is formed as a dye-proof layer for protecting the first color filter 54 from being dyed by yellow dyeing material on the entire surface of the flat layer 40 and the first color filter layer 54. The first inter-layer 56 is formed of a positive polyimide.
After forming the first inter-layer 56, the second filter layer 58 of yellow layer is formed on the first inter-layer 56 corresponding to the second and the third photodiodes 34 and 36.
In order to prevent the second color filter layer 58 from being dyed by cyan material, a second inter-layer 60 of positive polyimide is formed on the entire surface of the first inter-layer 56 and the second color filter layer 58. A third color filter layer 62 of cyan layer is formed at the position corresponding to the third photodiode 36 disposed on the second inter-layer 60. The overlapped portion 66 of the second color filter layer 58 and the third color filter layer 62 has green color.
In order to protect the third color filter 62 from an external impact, a third inter-layer 64 of positive polyimide is formed on the entire surface of the second inter-layer 60 and the third color filter layer 62. Thereafter, for the purpose of wire bonding, the flat layer, the first, the second and the third inter-layer 56, 60 and 64 formed as above-described are removed at a time by photo-etching process so as for the pad area 52 to be exposed.
In the manufacturing method color filter on the IT-CCD as described above, as for the complementary color type with an improved color sensitivity, it is noted that cyan layer and yellow layer are mutually overlapped in order to form green layer. That is, the first, the second and the third color filter layers 54, 58 and 62 are formed on the IT-CCD, and inter-layer 56, 60 and 64 are formed as a transparent dye-proof layer for prevent the colors from mixing in the color filter layer.
Recently, as the light receiving part is being decreased in accordance with the high-efficiency of the IT-CCD, the area per unit pixel is in a tendency toward reduction. Accordingly, the allowance margin against a defect in the inter-layer and the align accuracy for the color filter layer is also reduced.
Such a need causes defects for the inter-layer in thermal hardening process. That is, in the thermal hardening process carried out each time after forming each color filter layer, the inter-layer is deformed due to a thermal shrinkage, resulting in a possibility that the color filter layer would be moved or the inter-layer would be cracked.
For the purpose of avoiding it, there has been used a process in which inter-layer is made by stacking different material each other, nevertheless, a problem still remains as far as concerned the thermal shrinkage according to the hardening process for the color filter layer. In particular, the inter-layer is formed of a positive polyimide which is widely used because of its excellent light transmissivity. However, even the material has severe thermal shrinkage in its characteristic, so that a stress is acted on the interface between the color filter layer and the inter-layer, causing the movement of the color filter layer and even the image defect such as a wave trace or white blot due to a crack of the inter-layer, resulting in degrading the characteristic of the image sensor.